I guess if you were talking definitively, it would be stuff like Hendrix, Beatles etc. But there are so many things that contribute to making a gig enjoyable - who you're with, sound, venue, what you've taken/ drank/ smoked/ sniffed etc. So I guess it's quite personal innit. All the best ones that I can think of are quite recent. because I have a shit memory.

I also quite liked Ben Kweller last year at Islington and T
Bright Eyes this week
Radiohead in Cardiff
Willy Mason at the Borderline
The Zutons and Elbow at Shepherds Minge last year
Battle supporting Bloc Party the other week
REM at Hammersmith last year
The Strokes, Muse, and the rest of the line up T in the Park
Franz Ferdinand at Astoria a while ago
Sleepy Jackson at Astoria a while ago too.

I didnt like (and walked out of)
Embrace last year
The Thrills this year
Kasabian last year

Oh! To be young and full of wit. Just wait young man. Soon you'll be old and bitter and remenisceing the good old days when the Libertines were playing the local pub. BTW, I'm pretty sure the first Can show was in Munich and it was in '69.

see what I mean, this thread has inspired me to get my pile of ten years worth of gig tickets (full on nostalgia fest) and I've already found two that need to be added:
Rage against the machine @ Brixton Academy, 1996
Beastie Boys @ Brixton Academy, 1997